I have an application which uses MPI_Allgather with derived types. It works correctly with mpich2 and mvapich2. However it crashes periodically with openmpi2. After investigation I found that the crash takes place when I use derived datatypes with MPI_AllGather and number of ranks greater than 8. I’ve written a simple application which demonstrates the crash. It simply calls for MPI_Allgather with derived datatype that consists of 1 shifted integer . The sample works correctly with number of ranks 2-8. But when number of ranks is greater than 8 it crashes with segmentation fault inside MPI_Type_free, MPI_Allgather or MPI_Type_create_struct functions. This sample also works correctly with mv2, mpich2 with any number of ranks. Is this a limitation of ompi allgather?